Python string.format() 没有四舍五入的百分比
声明：本页面是StackOverFlow热门问题的中英对照翻译，遵循CC BY-SA 4.0协议，如果您需要使用它，必须同样遵循CC BY-SA许可，注明原文地址和作者信息，同时你必须将它归于原作者（不是我）：StackOverFlow
原文地址: http://stackoverflow.com/questions/17610698/
Warning: these are provided under cc-by-sa 4.0 license. You are free to use/share it, But you must attribute it to the original authors (not me):
StackOverFlow
Python string.format() percentage without rounding
提问by Ashy
In the example below I would like to format to 1 decimal place but python seems to like rounding up the number, is there a way to make it not round the number up?
在下面的示例中，我想格式化为小数点后 1 位，但 python 似乎喜欢四舍五入，有没有办法让它不四舍五入？
>>> '{:.1%}'.format(0.9995)
'100.0%'
>>> '{:.2%}'.format(0.9995)
'99.95%'
采纳答案by Martijn Pieters
If you want to round down always(instead of rounding to the nearest precision), then do so, explicitly, with the math.floor()function:
如果要始终向下舍入（而不是舍入到最接近的精度），请使用以下math.floor()函数显式执行此操作：
from math import floor
def floored_percentage(val, digits):
val *= 10 ** (digits + 2)
return '{1:.{0}f}%'.format(digits, floor(val) / 10 ** digits)
print floored_percentage(0.995, 1)
Demo:
演示：
>>> from math import floor
>>> def floored_percentage(val, digits):
... val *= 10 ** (digits + 2)
... return '{1:.{0}f}%'.format(digits, floor(val) / 10 ** digits)
...
>>> floored_percentage(0.995, 1)
'99.5%'
>>> floored_percentage(0.995, 2)
'99.50%'
>>> floored_percentage(0.99987, 2)
'99.98%'
回答by danodonovan
There are a couple of ways, maybe the easiest is
有几种方法，也许最简单的是
x = str(10. * 0.9995).split('.')
my_string = '%s.%s%%' % (x[0], x[1][:2])
this will ensure that you always have the decimal point in the correct place (for edge cases like 1.0000or 0.001)
这将确保您始终将小数点放在正确的位置（对于像1.0000或这样的边缘情况0.001）
回答by Ashwini Chaudhary
Something like this:
像这样的东西：
def my_format(num, x):
return str(num*100)[:4 + (x-1)] + '%'
>>> my_format(.9995, 1)
'99.9%'
>>> my_format(.9995, 2)
'99.95%'
>>> my_format(.9999, 1)
'99.9%'
>>> my_format(0.99987, 2)
'99.98%'
回答by jpp
With Python 3.6+, you can use formatted string literals, also known as f-strings. These are more efficient than str.format. In addition, you can use more efficient floor division instead of math.floor. In my opinion, the syntax is also more readable.
在 Python 3.6+ 中，您可以使用格式化的字符串文字，也称为 f 字符串。这些比str.format. 此外，您可以使用更高效的楼层划分来代替math.floor。在我看来，语法也更具可读性。
Both methods are included below for comparison.
两种方法都包含在下面以进行比较。
from math import floor
from random import random
def floored_percentage(val, digits):
val *= 10 ** (digits + 2)
return '{1:.{0}f}%'.format(digits, floor(val) / 10 ** digits)
def floored_percentage_jpp(val, digits):
val *= 10 ** (digits + 2)
return f'{val // digits / 10 ** digits:.{digits}f}%'
values = [random() for _ in range(10000)]
%timeit [floored_percentage(x, 1) for x in values] # 35.7 ms per loop
%timeit [floored_percentage_jpp(x, 1) for x in values] # 28.1 ms per loop
